Use of chemical sensors to detect ultra-trace analytes from explosives has been the focus of investigation in recent years owing to the critical importance of detecting explosives in a wide variety of areas, such as mine fields, military bases, remediation sites, and urban transportation areas Detecting explosive analytes also has obvious applications for homeland security and forensic applications, such as the examination of post-blast residue. Typically these chemical sensors are small synthetic molecules that produce a measurable signal upon interaction with a specific analyte.
Chemical sensors are preferable to other detection devices, such as metal detectors, because metal detectors frequently fail to detect explosives, such as in the case of the plastic casing of modern land mines. Similarly, trained dogs are both expensive and difficult to maintain. Other detection methods, such as gas chromatography coupled with a mass spectrometer, surface-enhanced Raman, nuclear quadrupole resonance, energy-dispersive X-ray diffraction, neutron activation analysis and electron capture detection are highly selective, but are expensive and not easily adapted to a small, low-power package.
Conventional chemical sensors have drawbacks as well. Sensing TNT and picric acid in groundwater or seawater is important for the detection of buried, unexploded ordnance and for locating underwater mines, but most chemical sensor detection methods are only applicable to air samples because interference problems are encountered in complex aqueous media. Thus, conventional chemical sensors are inefficient in environmental applications for characterizing soil and groundwater contaminated with toxic TNT at military bases and munitions production and distribution facilities. Also, conventional chemical sensors, such as highly π-conjugated, porous organic polymers, are commonly used as chemical sensors and can be used to detect vapors of electron deficient chemicals, but require many steps to synthesize and are not selective to explosives.
Furthermore, many conventional chemical sensing methods are not amenable to manufacture as inexpensive, low-power portable devices. Additionally, these methods are limited to vapor phase detection, which is disadvantageous given the low volatility of many explosives. For example, the vapor pressure of TNT, which is approximately 5 ppb at room temperature, may be up to six times lower when enclosed in a bomb or mine casing, or when present in a mixture with other explosives.
Additionally, current routes for synthesis of polymetalloles use hazardous reagents and are of low efficiency. For example, poly(tetraphenyl)silole has been synthesized by Wurtz-type polycondensation, but the reaction yields are low.